Field of the Invention
This invention relates to a method of continuously forming or depositing a thin film on a polymeric film, i.e. forming a polymer film, by vacuum deposition, i.e. via vacuum evaporation.
A typical conventional method of forming a thin metal film on a polymeric film at a high productivity rate is a vacuum deposition method. FIG. 5 schematically shows an internal structure of such a vacuum deposition apparatus commonly used for the production of a thin film. A polymeric film 1 is transported around a cylindrical can 2 or travels circumferentially on the outer peripheral surface of the cylindrical can 2 in a direction indicated by arrow A. A thin film is deposited on the polymeric film 1 from an evaporation source 5. Reference numerals 3 and 4 denote a supply roll of the polymeric film 1 and its take-up roll, respectively. Reference numerals 9 and 10 denote free rollers. As the evaporation source 5, for example, a resistance-heating evaporation source, an induction-heating evaporation source or an electron beam evaporation source can be used. A shield plate 6 is provided between the evaporation source 5 and the cylindrical can 2 so as to prevent the vapor from the evaporation source 5 from depositing on unnecessary portions. The shield plate 6 has an opening S for allowing vapor to pass therethrough to be deposited on the polymeric film 1. When a thin film is to be produced by vacuum deposition at a high deposition rate, the polymeric film is susceptible to thermal deformation and thermal decomposition due to radiation heat from the evaporation source and condensation heat of the evaporated atoms. Therefore, in order to avoid such thermal damages during the formation of the thin film at a high deposition rate, it is necessary that the polymeric film 1 be disposed in intimate contact with the outer peripheral surface of the cylindrical can 2 so as to efficiently transfer the heat, received by the polymeric film 1, to the body of the cylindrical can 2. One method of keeping the polymeric film 1 in intimate contact with the outer periphery of the cylindrical can 2 is to apply an electron beam 7 from an electron gun 8 to the polymeric film 1 disposed in contact with the outer periphery of the cylindrical can 2, so that electrons penetrate into the polymeric film 1 to produce an electrostatic attractive force between the polymeric film 1 and the cylindrical can 2, thereby keeping them in intimate contact with each other. Generally, a pierce-type electron gun which can scan a wide range is used as such an electron gun. After the thin film is formed on the polymeric film 1, the polymeric film 1 is still kept highly charged electrostatically. When the polymeric film 1 is kept charged, it is difficult to cause the polymeric film 1 to travel in a stable manner. For this reason, usually, the polymeric film 1 is subjected to a glow discharge treatment so as to eliminate the electrostatic charge from the polymeric film. This glow discharge treatment is effected by a glow discharge electrode 11 and gas which is introduced into a vacuum chamber.
When the thin film is to be formed by the above conventional method using the vacuum deposition apparatus, i.e. vacuum evaporation apparatus, of FIG. 5, there is encountered a problem in that where the cylindrical can is at elevated temperatures or the degassed polymeric film is used, wrinkles are liable to develop on the polymeric film during the step of applying the electrons to the polymeric film. Another problem is that the strength of bonding between the resultant thin film and the polymeric film is not adequate. Further, when the thin film is formed directly on the polymeric film, the characteristics or properties of the thin film, in some cases, have been found not satisfactory because of the influence of the polymeric film.